To satisfy physical properties, such as scratch resistance and hardness, of an ultrathin film coated on a substrate (film base), ultraviolet curing comprising applying an ultraviolet curable resin to a substrate and curing the resin by irradiation with ultraviolet light has been employed. Further, to promote curing by ultraviolet light, various methods have been proposed.
For example, in Patent Document 1, to facilitate curing of a coated film, an ionization radiation curable coated layer is formed and then an ionization radiation is applied with winding a substrate around a heating roll and heating to 30 to 100° C. together with the coated layer.
Further, Patent Document 2 discloses a method in which a transparent release film is applied to a coated surface in view of the fact that oxygen prevents ultraviolet curing. Patent Document 3 discloses a method of improving hardness by decreasing oxygen concentration by evacuating the target atmosphere for ultraviolet irradiation. Patent Document 4 discloses controlling the oxygen concentration in the target atmosphere for ultraviolet irradiation to 1000 ppm or lower and replacing oxygen dissolved in a coating solution with inert gas. Patent Document 5 discloses UV irradiation of a coated film formed on a base in a thickness of 0.005 to 1 μm in an O2 concentration of 1000 ppm or lower. Further, Patent Document 6 discloses controlling the amount of inert gas supplied to an electron beam irradiation device in an apparatus for curing by electron beam irradiation under a reduced O2 concentration. Patent Document 7 discloses a method for reducing O2 concentration in both a coating zone and a UV irradiation zone. Patent Document 8 discloses an apparatus in which a uniform hardness is maintained while the consumption of inert gas is reduced. Patent Document 9 discloses a method in which cooling air is supplied while controlling the static pressure in a UV lamp so as to maintain a low O2 concentration in an ultraviolet irradiation device.
As described above, it has been conventionally attempted to decrease the O2 concentration in an irradiation device of ionization radiation or increase the temperature of coated film so as to facilitate curing of the coated film.    [Patent Document 1] Japanese Patent Publication No. 7-51641    [Patent Document 2] Japanese Patent Laid-Open No. 56-139176    [Patent Document 3] Japanese Patent Laid-Open No. 5-186509    [Patent Document 4] Japanese Patent Laid-Open No. 8-152517    [Patent Document 5] Japanese Patent Laid-Open No. 11-104562    [Patent Document 6] Japanese Utility Model Laid-Open 7-17365    [Patent Document 7] Japanese Patent Laid-Open 2000-343022    [Patent Document 8] Japanese Patent Laid-Open No. 11-268240    [Patent Document 9] Japanese Patent Application No. 2003-034076